The present invention generally relates to a wiring film; and more particularly, the invention relates to a wiring film for transistors and a method for forming such a wiring film.
Heretofore, low-resistance materials (such as, Al, Cu, etc.) have been used in metallic wiring films for electric parts. For instance, in the case of the TFT (Thin film transistor) liquid crystal displays, a demand for the reduction in the resistance of the wiring electrodes has been increasing with the enlargement of the panels, and the necessity for using Al and Cu as the low-resistance wirings has been growing.
When an Al wiring including Al as a major component is in contact with an oxide (such as, SiO2, ITO (indium tin oxide) or the like), hillock may be formed by oxygen of the oxide. Furthermore, when the Al wiring is used as source and drain electrodes of a TFT, there are problems of diffusion into an underlying Si layer and a degradation in contact resistance between a transparent electrode made of ITO.
On the other hand, as to the Cu wiring, Cu is a material having a lower resistance than that of Al. Although degradation in the contact resistance between Al and the ITO transparent electrode poses a problem, copper oxide exhibits an excellent contact resistance because it has less insulating than aluminum oxide.
Therefore, a need to use Cu for low-resistance wiring films has been increasing. However, as compared to other wiring materials, there are problems in that Cu has poor adhesion to underlying materials (such as glass, Si or the like) and in that Cu diffuses into the Si layer when it is used as the source and drain electrodes. Thus, a barrier layer is required at an interface between the Cu wiring and other layers so as to enhance the adhesion and prevent the diffusion. With regard to an underlying Cu seed layer made of a Cu plating, which is used for a semiconductor, a barrier layer made of TiN, TaN or the like is required to prevent the diffusion from the view point of the same diffusion problem as mentioned above.
As to related patents on metallic wiring films including Cu as a major component for electronic parts, a technique characterized by adding an element (such as, Mo or the like) into Cu (JP-A 2005-158887) and a technique characterized by introducing nitrogen or oxygen during a film forming method by sputtering pure Cu (JP-A 10-12151) are known. However, both of the above-mentioned conventional techniques have problems in adhesion, reduction of resistance, and formation of hillock.
The present invention has been accomplished in order to solve the above-mentioned problems; and the object of the present invention is to provide a low-resistance wiring film having high adhesion to the glass substrate and the silicon layer.